The present invention relates to a device for transferring a signal between two end points between which a coiled conductor which is contained in a substantially circular cassette is arranged, and to which further extending conductors can be attached at the two end points, the length of the conductor being substantially greater than the distance between the two end points, and wherein at least one of the two end points is movable relative to the other, the cassette consisting of two parts, namely a stationary stator and a turnable rotor.
Such a device is described in European patent document EP-OS 0 417 350.
Such a device is needed, for instance, for transmitting a signal for releasing the collision-protection "air bag" of motor vehicles. It is arranged in the steering wheel of a motor vehicle for the transmission of an electrical or optical signal. "Conductor", as used in the invention, can therefore be an electrical conductor or an optical conductor. One essential problem in the case of this device is the transmission of a signal between stationary and moving parts of the motor vehicle. The wiper contacts or rings known for a long time for the transmission of current in such cases are subject to wear and are disadvantageous, particularly in the case of low current intensities due to the varying contact resistances.
In the known device according to the aforementioned EP-OS 0 417 350, electric current is used for the transmission of the signal. The transmission of the signal is effected by a ribbon conductor coiled, for instance, in the manner of a spring housing. Upon relative rotation of the two end points connected by the ribbon conductor, the coiled ribbon conductor "breathes" like the spring of a watch. The turns of the coiled ribbon conductor are contracted to a smaller diameter in one direction of rotation. In the opposite direction of rotation, they again return to a larger diameter. It is therefore important, for the installing of this device in the steering wheel of a motor vehicle, that the two end points have a very specific position with respect to each other with a corresponding position of the ribbon conductor, so that the predetermined rotations of the rotor are possible in both directions of rotation of the steering wheel without the ribbon conductor being torn off from the end points or otherwise damaged.